In image-formation apparatuses, such as photocopiers and printers, to which electrophotographic technologies are applied, many organic photoreceptors are employed, each of which has a sensitivity to light emitted from a light-source in the apparatus within a range of wavelength of the light. It is known that the organic photoreceptor includes monolayer type photoreceptors and multilayer type photoreceptors. The monolayer type photoreceptor comprises a single photoreceptor layer wherein a charge generating material and a charge transferring material have been dispersed in a thin film of an appropriate binder resin. The multilayer type photoreceptor comprises a charge generating layer comprising a charge generating material; and a charge transferring layer comprising a charge transferring material, wherein the charge generating layer and the charge transferring layer are laminated.
Conventional phthalocyanine compound has a spectral sensitivity to a light having a long wavelength or less, good charge generation efficiency, good fastness, high sensitivity and high durability. Therefore, various phthalocyanine compounds are employed as charge generating materials. Among others, titanylphthalocyanine can be used in an electrophotographic photoreceptor, since the titanylphthalocyanine has characteristics such as high charging amount and high sensitivity, and the titanylphthalocyanine can be easily formed into a thin film, such as a charge generating layer, by vapor deposition or dispersing.
These phthalocyanine compounds have considerably different electric characteristics depending on each stacking state even though they have the same molecular structure. Stacking state of the organic compound molecule is determined by its polymorph. Therefore, different polymorph provides different stacking state. Accordingly, perturbation of electron in π electron system is altered. This is why that the characteristics in an electronic material such as an organic photoreceptor can be significantly altered.
Generally, titanylphthalocyanines can be produced by an urea synthetic method (i.e., Weiller method) or a phthalonitrile synthetic method. These conventional methods, however, immediately after the synthesis, often provide a crude titanylphthalocyanines containing various polymorphs, such as “β-form”, “α-form” and other metastable polymorphs, i.e., a polymorphic mixture. Since the polymorphic mixture is a mixture of crystals each of which has different electric characteristics, the conventional titanylphthalocyanines are not suitable for applying them to a charge generating material such as an electrophotographic photoreceptor.
Therefore, in the art, titanylphthalocyanine having a suitable single polymorph has been investigated in order to use the titanylphthalocyanine, as starting material, as it is a crude, suitable for producing a charge generating material. Examples of such attempts include the followings.
Patent Literature 1: JP-A-61-239248 discloses a method for producing an α-form titanylphthalocyanine having a peak at a Bragg angle (2θ±0.2°) in X-ray diffraction spectrum with CuK α-ray: 7.5°, 12.3°, 16.3°, 25.3° and 28.7°, which includes preparation of a crude α-form titanylphthalocyanine according to a phthalonitrile synthetic method; washing the crude titanylphthalocyanine with acetone by means of a Soxhlet's extractor; dry milling the washed titanylphthalocyanine in the presence of alumina beads. This method employs a Soxhlet's extractor. Therefore, the equipments for the synthesis are complicated. The method includes vigorous washing with a solvent with heating. Therefore, such procedure is complicated. Totally, the disclosed method is not a convenient for producing an α-form titanylphthalocyanine.
Patent Literature 2: JP-A-8-209023 discloses a method of transformation including subjecting a low crystalline titanylphthalocyanine resulted from an acid pasting treatment to milling with zirconia beads in the presence of dichlorotoluene, sodium chloride and water to prepare a crystal thereof having a peak at a Bragg angle (2θ±0.2°) in X-ray diffraction spectrum with CuK α-ray: 7.22°, 9.60°, 11.60°, 13.40°, 14.88°, 18.34°, 23.62°, 24.14° and 27.32°. This method, however, includes a complicated steam distillation in order to remove the dichlorotoluene. There may be a problem that the resulting photosensitive characteristics of the titanylphthalocyanine are deteriorated, if the resulting titanylphthalocyanine is contaminated with any inorganic salt such as sodium chloride. Therefore, many water-washing procedures are required. Totally, the disclosed method is complicated.